1. Field of the Invention
The present invention is related to a method for controlling soft-start and related apparatuses, and more particularly, to a method for dynamically controlling soft-start and related apparatuses.
2. Description of the Prior Art
A digital pulse width modulation (PWM) circuit is often used in a back light boost converter. The PWM circuit determines whether to continue on outputting control signals to an analog circuit according to feedback signals of an analog circuit, so as to control a boosting procedure. In general, a soft-start mechanism is applied when the digital PWM circuit starts, in order to provide a specific pulse during the boosting procedure. The specific pulse has a fixed frequency, and a slowly increasing, long lasting duty cycle. The value of the specific pulse is related to application conditions and external unit values. Therefore, a power-on impulse current caused by an adding effect of inductance current can be prevented, and influences on designs of system circuits and power managements caused by electromagnetic interferences (EMI) can be avoided.
Please refer to FIG. 1, which illustrates a schematic diagram of a prior art back light boost converter 10. The back light boost converter 10 comprises a digital PWM controller 12 and an analog circuit 14. The analog circuit 14 comprises components such as resistors R, inductors L, capacitors C, diodes D, impedances Z, transistors Q, etc, and can generate a switch signal VLED and a feedback signal FB according to a pulse signal DRV for controlling a back light module. The PWM controller 12 generates a pulse signal DRV for controlling the analog circuit 14 according to the feedback signal FB.
In the prior art, soft-start time of the back light boost converter 10 is fixed. Unlike an analog PWM controller providing linearly increasing switch signals, the digital PWM controller 12 provides the switch signal VLED with duty cycles increasing by steps, so that when the back light module adjusts the switch time dynamically, the digital PWM controller 12 of the prior art is not able to achieve the soft-start mechanism using fixed time.